Millions of people knew Carl Sagan as "their" guide to the cosmos. The collection of essays in "Carl Sagan's Universe" will help all of us appreciate his other achievements which continue to enrich humankind.

The book was meant to be a record of the symposium that honored Sagan's 60th birthday in October 1994. With his sudden death two years later, the updated essays by many of Sagan's colleagues now become a tribute to the many dimensions of his legacy. They put his contributions into the perspective of what has been achieved and where the work is going.

Sagan was a vigorous proponent of cosmic exploration, whether by telescope or by spacecraft. He helped launch the search for life, or conditions that might support life, beyond Earth.

As Wesley Huntress notes, Sagan asked the big question at the beginning of the space age: Are we alone in the universe? Soon to retire as associate administrator for space science at the National Aeronautics and Space Administration, Mr. Huntress adds: "In my view, the mission of this country's space exploration enterprise ... is to explore the universe, to seek out new planets, and to search for life elsewhere in the galaxy." Sagan's colleagues bring us up to date on the progress of that search.

Sagan was also enthusiastic about - and concerned for - life on Earth. His work on arms control helped lessen the threat of nuclear war. He used his scientific expertise and his persuasive power to drive home the point that full-scale nuclear war would be a global catastrophe. He was a chief architect of the theory of nuclear winter - the prospect that such a war would throw up enough dust and smoke to block sunlight and plunge Earth into years of unremitting, plant-killing cold. He maintained a drum beat of reasoned argument in Washington to end nuclear weapons testing.

Geophysicist Richard Turco of the University of California at Los Angeles, who worked with Sagan on these issues, says: "It is clear to me, that the strength of Carl's will, his broad scientific training and genuine creativity, and his deep concern for the welfare of the human species ... have helped in a substantial way to draw civilization back from the brink of nuclear self-destruction."

Sagan was not a religious man in the traditional sense. Asked if he thought God exists, he replied that, if the concept of God meant "the sum total of the laws of Nature," then he thought God exists. Otherwise, he found the concept too vague to have substantial meaning. Nevertheless, his outreach to the religious community wrought a breakthrough in mindsets that launched an on-going discussion between scientists and religious thinkers on how to preserve our planet.

He persuaded 32 other scientists to join in "An Open Letter to the Religious Community." In it, they made the point that cherishing and maintaining our planetary home is as sacred a mission as any the churches have historically embraced.

To those who objected to the scientists' evolutionary point of view, Sagan replied that "we do not have to agree on how the natural world was made to be willing to work together to preserve it."

Joan Campbell, general secretary of the National Council of the Churches of Christ, calls that letter "the catalytic event that led to the permanent, irreversible integration of environmental issues into mainstream American religious thought and life."

Sagan as catalyst: That's what emerges from these essays. He inspired workers in divers fields to labor harder for the benefit of all humankind.